How Much weight could you lose in 2 hours of exercise?

The simple answer is that you burn about 100 calories per mile running, 120 calories per mile cycling or swimming. So multiply the burn rate per mile by the total number of miles you can do in two hours. Running at a moderate pace of 4 miles per hours you would burn:

100 × 4 × 2 = 800 calories

1 pound of fat has an energy value of 3500 calories, so you would lose just under a quarter of a pound of fat running for two hours at moderate speed.

The more complicated answer would depend on the size you are and the intensity of the exercise that you do. Age, height and body shape are also important, but to makes things simple, these will not be considered.

Body size or mass:

The more you weigh, the more calories are required to move you. So a 110 pound female would burn more calories than a 100 pound female running the same distance and at the same speed.

Intensity

1) Your body will burn calories in accordance to the exercise you are currently doing. i.e. running, weight training, swimming and cycling.

2) Depending on how hard you trained, your body will continue to burn fuel after you finished exercising. Your muscles generate a lot of heat when exercising, so your body will use energy to try and cool you down. Exercising also produces toxins such as lactic acid, and damages muscle fibres which need repairing.

Your body will in affect speed up after workout. It does this to cool you down, get rid of toxins and repair muscle tissue.

If you train as hard as you can for the two hours using as many muscles as you can, it is possible to burn same amount of calories after your workout as you did in your workout. So using running as am example, you would burn 800 calories during the run, and 800 calories after the run. 1600 calories is equal to about ½ pound of body fat. However you would need to sprint within you run for periods and run up and down hills to burn as much after workout as you did within your workout.

After a workout feel your muscles so see how hot they get. The hotter they get the harder they worked and and the harder they will continue to work after.

As my example and not part of the answer

When I did jungle training in the army, I was burring 10,000 calories a day. I know that sounds hard to believe but it is true. I carried around 100 pounds in weight, and was covering 5 miles an hour in tropical temperatures. I was losing two pounds of body weight per day, even when eating 5000 calories a day.